The present invention relates to a guard rail construction, comprising support elements to be provided at a side of a road and a guard member attached hereto, wherein, when a vehicle couches the guard member in and adjacent the collision point thereof, one or more support elements can pivot in rearward direction relative to the road about a pivot point and can absorb at least a part of the collision energy, while the guard rail construction can pivot in rearward direction to such an extent that it can be supported on the ground by a support point.
Such guard rail constructions are known and have presently been installed alongside many Dutch roads. In these constructions, guard members in the form of guard rails have been provided symmetrically on either side of the support element. The center of the guard member against which a collision takes place will hereinafter be referred to as the collision point. When a vehicle contacts a guard rail, the support element will make a rearward tilting movement. The point about which the support element moves rearwards will hereinafter be referred to as the pivot point. On bridges, this pivot point is at the ground level, by means of a break connection. In the guard rail constructions mentioned, the height of the center of the guard rails, i.e. the distance at which the collision point lies above the ground level, is about 60 cm. The overall height of the system, i.e. the distance from the top side of the guard rail to the ground level, is about 75 cm. The system is further determined by, inter alia, the angle xcex1 made by the line between the pivot point and the collision point with the ground level. When the pivot point lies approximately at ground level, a situation which, as mentioned hereinabove, may occur when the guard rail construction is installed on, for instance, bridges, this angle xcex1 will be about 56xc2x0. When in this situation the guard rail construction during a collision moves rearwards about the pivot point, the height thereof increases at first by about 11%, to subsequently decrease until eventually approximately the same level is reached which the guard rail construction had before the collision. The guard rail mounted on the side of the support element other than the side of the guard rail against which the vehicle has collided, will then in many cases, after tilting of the support element through an angle xcex2 of about 52xc2x0, be supported on the ground. The point of the guard rail construction by which it can be supported on the ground after a collision will hereinafter be referred to as the support point. The angle xcfx86 between the line through the pivot point and the collision point and the line through the pivot point and the support point will, in the case where the pivot point is at the ground level, be about 76xc2x0.
In the guard rail construction here mentioned, the vehicle may, during a collision, contact the support element. In particular for heavier vehicles, where the point of gravity lies above the level of the guard rail construction, this will involve the serious risk that, due to the rolling behavior about the longitudinal axis of the vehicle occurring during the collision against the guard rail construction, the vehicle actually rolls over the guard rail construction.
A contact of the vehicle with the support element can be prevented by providing that the pivot point comes to lie below the ground level, which, in practice, is in fact realized along roads over the ground. In that case, the pivot point lies about 60 cm below the ground level. The angle xcex1 then approximately assumes the value of 72xc2x0. When, during a collision, the guard rail construction moves rearwards, with the support element moving for a substantial part through the ground, a slight height increase of about 5% occurs at first, whereupon the height of the system decreases to below the original value by about 7%. Further, due to the larger distance between the pivot point and the guard rails, a greater rearward travel is made by the guard rail construction and, accordingly, the space required for the proper functioning increases considerably. When the rearmost guard member finds support on the ground, the support element will approximately have pivoted through an angle xcex2 of about 40xc2x0, which value is considerably less than in the case where the pivot point lies at the ground level. It is true that by positioning the pivot point below the ground level, the chance of a colliding vehicle touching the support element decreases, but the danger of tilting of the vehicle is not reduced at all.
The object of the invention is to avoid the above-mentioned drawbacks, or at least to reduce them to a considerable extent, and to provide a guard rail construction wherein the chance that vehicles, during a collision, can roll over the guard rail construction is reduced substantially, without the guard rail construction in its fixed arrangement being in a higher position and thereby hindering or even blocking the view of the lateral side of the road and without affecting the beauty of the landscape too much.
To realize this object, the guard rail construction as described in the preamble is characterized in that the angle xcfx86 between the line through the pivot point and the collision point and the line through the pivot point and the support point is greater than 90xc2x0.
Due to this feature, it is achieved that a vehicle colliding against the guard rail construction will not contact the support element. Further, during a rearward pivoting movement of the guard member that is contacted by the vehicle, the height,of this guard member can only increase. As or just before the moment when the guard member reaches its highest point, the guard rail construction will be supported on the ground. Through a suitable dimensioning, this height increase during a collision may run up to as much as 25% and more. Due to this rising movement of the guard member, a couple is exerted on the colliding vehicle, which couple opposes the couple which, during the collision, is exerted on the vehicle by the guard member and causes the vehicle to tilt in the direction of the guard rail construction. The effect further achieved is that for performing a rearward pivoting movement, relatively little extra space is needed.
Although a guard member may be present on both sides of the support element, in the guard rail construction according to the invention it is sufficient when such guard member is present only on the road-facing side of the support element.
To effect a substantial height increase during the rearward pivoting movement of the guard rail construction, the pivot point preferably lies at or relatively close below the ground level.
For stability reasons, it is preferred that the angle xcex2 through which the support element can pivot before the support point comes to lie on the ground, be less than 45xc2x0. For the same reason, it may be favorable when the support point is located at a lower position than the bottom side of the guard member. However, it is possible to lower the bottom side of the guard member or, stated differently, to extend the guard member downwards, for instance for retaining motorcyclists who come to fall; in that case, the support point may come to lie above the bottom side of the guard member all the same.
Although it is possible that the collision energy that is absorbed at first is entirely taken up in the pivot point, for instance by designing this pivot point as a deformable pivot, it is preferred that a deformable element be mounted on the support element between the support point and the ground on which the support element can be supported. This element can then absorb a substantial part of the collision energy. When his element has been entirely deformed and the support element has virtually come to the ground by the support point, the entire construction forms a considerably stiffer whole and further energy will be absorbed in the support element itself and in the ground on which this element is supported.
In a particular embodiment, the support element is composed of a substantially upwardly directed first portion and, connected thereto, a second portion extending in the direction of the road, the guard member being attached to the second portion. Thus, the angle xcfx86 between the line between the pivot point and the collision point and the line between the pivot point and the support point can be chosen to be greater without the height of the guard rail construction increasing, while during a rearward tilting of the guard rail construction, a greater height increase can be realized. This construction further provides the possibility of designing the second portion so as to be displaceable in substantially rearward direction relative to the road, which allows this second portion to absorb a part of the collision energy. Of course, this would also have been possible if the second portion of the support element were of deformable design. In particular, it is favorable when the force at which the second portion can be displaced relative to the first portion is less than the force needed for compressing the deformable element under the support point. During slight collisions, the collision energy can then be entirely absorbed by said second portion, while during heavy collisions, a portion thereof is first absorbed in the second portion and the remaining part thereof is absorbed by the rearward movement of the entire support element and eventually by the substrate on which the support element is then supported.
In particular when the deformable element has a frustoconical shape whose portion having the greatest section lies directly below the support point on the support element, the forces acting thereon are readily absorbed through deformation. Although the deformable element could also have, for instance, a cylindrical shape, this shape is less desired; since a cylinder is more inclined to buckle.
In a concrete embodiment, the support element consists of two shell parts. The deformable element. may form an integral part of the support element or be attached thereto separately.
Because of the essential role performed by the pivot point, the collision point and the support point in the guard rail construction according to the invention, it is favorable when the support element or the first portion thereof has a substantially triangular shape.
Although the support element can be manufactured from steel, from a cost viewpoint it is favorable when the support element is formed from a fiber-reinforced plastic or composite. In particular, a construction from two shell parts can easily be realized by a compression molding process. As a matter of fact, the guard member can be designed in many manners; it can be formed by various types of girders, round, square, etc., or by prestressed cables. In particular, the presently employed guard rails can be used for this. The guard members can also be manufactured from a fiber-reinforced plastic.